The present invention relates to a glass concrete, i.e. a concrete in which the aggregates wholly or partially consist of crushed glass, providing a particularly decorative appearance, which is desirable for facades etc.
The main elements of a concrete are cement, water, sand and stone. At production the sand and stone materials are divided in several fractions with respect to grain size. In addition it is common to add chemical and mineral components to obtain the required properties for the fresh and cured concrete.
xe2x80x9cGlass concretexe2x80x9d is known per se, and has been used for certain purposes where the aesthetical aspects have been a main consideration. The use of concrete with glass as aggregate is not however, free of problems, and it has not been possible to obtain a concrete that is nearly as good as concrete with conventional aggregates with respect to compressive strength and fracture strength. Neither does the present invention give directions of a glass concrete that is particularly well suited for constructional use.
A particular problem associated with glass in concrete is the presence of alkalies in the concrete and the thereby related problems. Since glass is alkali reactive and reacts with water soluble alkalies in the concrete, expansion will usually occur, causing fissures in the concrete. The problem is well known and attempts have been made to avoid it by using low alkali cement and different additives, but so far no successful solution has been found.
Swedish patent No. 501 419 teaches the use of recycle glass as a filler in concrete. With filler in this context is meant a (glass) fraction with grain sizes from 0-0.25 mm. The characterizing part of the patent is that 95% by weight of the glass filler used has a grain size less than 300 micrometer (0.3 mm). It is an object of the method according to this patent to provide a concrete that has good compressive strength and good properties with respect to workability of the fresh concrete. By using a filler with very fine grains it is possible to reduce the water content, which generally gives a better compressive strength for the finished, cured concrete. As shall be further elaborated below, however, the choice of grain size according to this patent implies a potential risk of alkali reactivity in the cured concrete, especially in cases where the concrete also includes alkali reactive aggregates.
For the manufacture of alkali resistant concrete, it is important that the total content of alkali is as low as possible. It is thus common to use low alkali cement with equivalent Na2Oxe2x89xa60.6%. In addition possible alkali content in the aggregates or additives must be taken into consideration.
The object of the present invention is to provide a product that is environmentally friendly and friendly with respect to the utilization of resources, by utilizing recycle glass as an aggregate to concrete for aesthetical purposes. More particularly it is an object to provide a glass concrete with best possible properties with respect to compressive strength and fracture strength. More particularly it is an object of the invention to eliminate the probably most severe disadvantage of glass concrete, namely the tendency of fissuration as a consequence of alkali reactions.